X11 has some fundamental problems. It's not fun using a modern desktop where it is impossible to sandbox individual applications. Firefox frequently processes untrusted data and is run with a dedicated uid, but it is also an interactive application and can suddenly listen in on all my passwords entered in other applications. Virtualized appliations are referred to using dumber protocols like VNC and SPICE which isn't always ideal.
Wayland has some interesting design issues on its own but that doesn't make the developers ignorant. XWayland will stick around for the foreseeable future.